(1) Field of the Invention
The present invention relates to a file sharing system and client apparatus and, more particularly, to a file sharing system and client apparatus that can take the advantages of both a Client/Server (C/S) type and a Peer to Peer (P2P) type.
(2) Description of the Related Art
As conventional file sharing systems, C/S type and P2P type file sharing systems are known. In the following description, a system file denotes a file that is managed by a file sharing system and accessible to a plurality of users and a local file denotes a file for private use that is managed by a client apparatus.
A conventional C/S type file sharing system is comprised of a file server and a plurality of clients connected to a communication network. In the C/S type file sharing system, when a client user wishes to make one of the user's local files open as a shared file, the client sends a file upload request to the file server. When the file upload is successful, the uploaded file is stored as a system file in the file server and the file server sends a file upload confirmation message to the requester client. When the client receives the file upload confirmation message, the shared file registration sequence is completed.
When a client user in the C/S type file sharing system wishes to access any open shared file, the client sends the file server a file download request designating the file identifier. In reply to the download request, the file server sends back the specified file to the requester client. The downloaded file is stored as a local file in the client apparatus.
On the other hand, the P2P type file sharing system is comprised of a management server and a plurality of clients connected to a communication network. In the P2P type file sharing system, when a client user wishes to register one of the user's local files with the sharing system as a shared file, the client sends a file registration request message to the management server. When the client receives a file registration acknowledgement message in which the file identifier is specified from the management server, the client stores a copy of the local file to be registered as a shared file into its storage as a system file and sends the management server a message to notify that the file saving has been completed. The management server registers the file identifier designated in the notification message into a management table as a new shared file, and returns an ACK message to the client. When the client receives the ACK message, the shared file registration sequence is completed.
When a client user in the P2P type file sharing system wishes to access any open shared file, the client sends the management server a file download request message designating the file identifier. Upon receiving the request message, the management server judges whether the specified file can be downloaded. If the file download is permitted, the management sever sends back the requester client a response message indicating the address of a client where the requested file is located. The requester client sends a file down load request to the client identified from the response message to receive and store the downloaded file as a local file.
As for the P2P type file sharing system, a distributed file management type system is proposed, e.g., in Japanese Unexamined Patent Publication No. 2004-5491. This system is arranged such that the management server manages directory information and each client can register a file with the sharing system by linking a system file stored in its storage to any folder represented by the directory information.